The present invention relates to a power semiconductor module. In particular, the invention relates to a power semiconductor module that may be suitably used for power conversion on an aircraft.
Power semiconductor modules are devices for converting and controlling the flow of electric energy and are used as inverters, DC/DC converters, and other power conversion devices. Power semiconductor modules are widely used in homes, industries, automobiles, aircraft, wherever power must be converted or controlled. Power semiconductor devices, including diodes, thyristors, power MOSFETS and IGBTs, are typically assembled to form power semiconductor modules, which may contain several such power semiconductor devices.
Controlling and converting power produces significant heat due to electrical losses in the power semiconductor devices. If not conducted away, this heat will increase the temperature of the power semiconductor module to the point of device failure. Power semiconductor devices are typically silicon based or silicon carbide (SiC) based. Silicon-based power semiconductors generally do not function beyond 150° C. SiC-based power semiconductors are able to function at much higher temperatures, as high as 250° C. They also have lower losses compared to their silicon-based counterparts and, as a result, SiC-based power semiconductors produce less heat. This combination of attributes means power semiconductor modules equipped with SiC-based power semiconductors should be able to function with smaller heat sinks and associated cooling systems, allowing the power semiconductor modules to be reduced in size and weight. However, thermal stresses resulting from cycling power semiconductor modules between on and off states, generally limit their operating temperature to 150° C. The thermal stresses result from the differences in coefficient of thermal expansion (CTE) between some of the power semiconductor module layers, such as copper and aluminum with CTE values of about 17×10−6/° C. and 25×10−6/° C., respectively, and AlN, Al2O3, silicon, and SiC with CTE values of about 4.3×10−6/° C., 7.3×10−6/° C., 3.2×10−6/° C., 4×10−6/° C., respectively. Failures modes include fracturing of the insulation substrate and delamination between layers with dramatically different CTEs. As a result, heat sinks and associated cooling systems cannot be fully reduced in size and weight to take advantage of the unique properties of SiC-based power semiconductors.
Recently, various configurations have been proposed using materials with CTE values that are significantly closer together to allow operation at temperatures approaching 200° C. However, none are able to closely match CTE values for all layers of a power semiconductor module to allow higher temperature operation, approaching 250° C., while reducing the weight of the power semiconductor module—an essential consideration for weight-sensitive applications, such as aircraft components.